1. Field of the Invention
The present invention relates to Ag—Bi-base alloy sputtering targets useful in forming Ag—Bi-base alloy films by sputtering, a method for manufacturing the sputtering targets, and a method for producing the Ag—Bi-base alloy films using the sputtering targets.
2. Description of the Related Art
Ag-base films (hereinafter, simply called as “Ag films”) made of pure Ag or Ag alloy are superior in optical properties such as high reflectance and high transmittance, and low extinction coefficient, superior in thermal properties such as thermal conductivity, superior in electrical properties such as low electrical resistivity, and are superior in surface fineness. Owing to these properties, the Ag films are widely used as reflective films, semi-transparent reflective films, and heat diffusion films for optical information recording media, reflective electrode films or interconnection films for flat panel displays, Low-E films for heat-ray reflecting/shielding glasses, shield films of shielding electromagnetic waves, and the like.
Numerous study on improvement of sputtering targets to be used in forming the Ag films having these superior properties has been made (see Japanese Unexamined Patent Publication No. 9-324264, and Japanese Unexamined Patent Publication No. 2000-239835). Japanese Unexamined Patent Publication No. 9-324264 discloses forming a sputtering target made of a silver alloy containing gold in the range of from 0.1 to 2.5 at % and copper in the range of from 0.3 to 3 at %, or of a silver-base composite metal is advantageous in preventing adverse effects by gas atmosphere such as oxygen supplied in sputtering, such as lowering of optic transmittance/optic reflectance in a short wavelength band of a visible rays range. Japanese Unexamined Patent Publication No. 2000-239835 recites setting a ratio in crystal orientation of the Ag sputtering target, namely, ((111)+(200))/(220) at 2.20 or more is effective in raising a sputtering rate, and accordingly, raising film production efficiency.
As mentioned above, the Ag films are superior in optical properties, thermal properties, and electrical properties owing to the aforementioned various improvements. Despite these superior properties, the currently available Ag films may encounter deterioration resulting from oxidation, corrosion, cohesion, peeling-off, or other factor in the case where applied products of the Ag films are placed in an environment of use for a long term. In view of this, there is a demand for securing stable, long-term use of the films.
For instance, pure Ag films obtained by sputtering of the conventional sputtering target have a multitude of crystal defects such as vacancy, dislocation, and grain boundary. Ag atoms may likely to easily migrate into these crystal defects. For example, if the pure Ag films are stored under a condition of high temperature and high humidity, Ag atoms may likely to migrate and cohere (condense) at the defective locations, with the result that the surface roughness may be raised and oversized growth of crystal grains may appear. Likewise, Ag atoms may likely to easily migrate and cohere (condense) in an environment containing halogen ions such as chlorine ions.
The inventors made an extensive study on securing stable, long-term use of Ag films, and filed a patent application identified by Japanese Patent Application No. 2002-361117. In this study, following is discovered: when prepared is a composite sputtering target constructed such that chips of various elements as additive elements are placed on a sputtering target made of pure Ag, and Ag—Bi-base alloy films are formed from such a composite sputtering target, the Ag—Bi-base alloy film such as Ag—Bi alloy films, Ag—Bi—Nd alloy films, Ag—Bi—Y alloy films, Ag—Bi—Cu alloy films, Ag—Nd—Au alloy films, Ag—Bi—Nd—Cu alloy films, Ag—Bi—Nd—Au alloy films, Ag—Bi—Y—Cu alloy films, and Ag—Bi—Y—Au alloy films is effective in preventing cohesion (aggregation) of Ag atoms in the presence of halogen ions, and in securing stable, long-term use of the Ag films.
However, as mentioned in the specification, there is a tendency that the Bi content in the film decreases, as compared with the Bi content in the sputtering target in forming the Ag—Bi-base alloy films. Further, a material damage such as cracking is found in a process of producing sputtering targets made of the Ag—Bi-base alloy comprising the steps of: melting Ag with Bi to produce ingots, and hot-working the ingots of Ag—Bi-base alloy. It is conceived that such a damage occurs because of low workability of the Ag—Bi-base alloy ingots.